1. Field of the Invention
The present invention relates to an air conditioning apparatus for car adapted to perform air conditioning and blast control in accordance with conditions of solar radiation.
2. Description of Prior Art
The air conditioning apparatus is known, which is adapted to detect conditions of solar radiation predominant within a car compartment such as a solar radiation intensity and a direction of solar radiation, then to perform air conditioning and/or blast control through a blast nozzle according to said conditions of solar radiation and thereby to optimize a distribution of conditioned air within the car compartment.
Such air conditioning apparatus of prior art is provided with a solar radiation detector comprising a light receiving element to detect solar radiation coming from the right side, a light receiving element to detect solar radiation coming from the left side of the car and a douser, and further provided with a controller adapted to control various air conditioning means on the basis of a detection value of said detector. Detection values I.sub.R, I.sub.L obtained from the right and left side light receiving elements of said solar radiation detector exhibit characteristics as indicated by broken lines in FIG. 22. It should be understood that the characteristics I.sub.R, I.sub.L were plotted, with respect to the sun at a constant height (.beta.=60.degree.), as the sunlight incident angle changes within a range (0.degree. through 90.degree.) between the front and the right side of the car and as the sunlight incident angle changes within a range (0.degree. through -90.degree.) between the front and the left side of the car, respectively. In general, the controller controls the various air conditioning means such as a mixing door and a blower on the basis of an arithmetically corrected value obtained from the detection values of solar radiation which vary as the solar incident angle on the respective light receiving elements.
Processing of the detection values to obtain the arithmetically corrected solar radiation value has conventionally been made in any one of following manners: (1) a higher one of the right and left detection values I.sub.R, I.sub.L is used as an arithmetically corrected value I.sub.0 as indicated by solid lines in FIG. 22; and (2) an arithmetic value (I.sub.R +I.sub.L)/.sub.9 is obtained as an arithmetically corrected solar radiation value I.sub.0 by using the right and left detection values I.sub.R, I.sub.L, as indicated by a solid line in FIG. 23.
With the solar radiation detector of prior art, however, both the light receiving element at the right side and the light receiving element at the left side of the car body are horizontally placed at least longitudinally of the car body. Accordingly, it is possible to detect the conditions of solar radiation so far as the sun is at a predetermined angle or higher, but when the radiation is incident on the light receiving elements from the lower sun, particularly from the front of the car body, the solar radiation detection values become too small to obtain an arithmetically corrected value of an appropriate level and therefore it will be difficult to achieve a desired air conditioning control at high accuracy.
When the method of arithmetic correction as set forth above in (1) is used, a relative sensitivity of the right side and the left side will be suddenly lowered. As a result, even when the car slightly changes its course right- or leftwards, the arithmetically corrected value I.sub.0 will largely change. Various parameters, for example, blast flow rate from the blower under a control based on such arithmetically corrected value I.sub.0 also suddenly change, deteriorating a comfortableness of air conditioning within the car compartment.
In the case of (2), on the other hand, the detection values of the respective light receiving elements (i.e., relative sensitivity) are low for relatively large solar radiation incident angles from right and left sides (larger than approximately 60.degree., -60.degree.), so appropriate correction of the solar radiation value and, therefore, air conditioning control based on particular conditions of solar radiation become difficult.
In view of such problems encountered by the air conditioning apparatus of prior art as have been mentioned above, the present invention is proposed hereby to solve them effectively.